No matter what paint you use, the biggest problem will be the residual gas that has soaked into the plastic. If you thin some fibeglass resin with acetone and give it a light coat, kind of like clearcoat, it should seal it well. Gas can seep out of the pores in the plastic later and ruin a good paint job. sometimes it takes months, sometimes only days. Even with the best paint, the residue seeping out will cause it to peel or bubble.